You must first remove all the telescope reference in your code before running composer remove laravel/telescope.

1. Check config/app.php, under providers array, remove the Telescope there.
2. Remove file app/Providers/TelescopeServiceProvider.php.
3. Remove telescope.php in config folder
4. Remove public/vendor/telescope
5. Remove file bootstrap/cache/config.php

Then finally you can run composer remove laravel/telescope.

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If you only want to stop running telescope, in file .env, set

TELESCOPE_ENABLED=false